1. Field of Industrial Utilization
The present invention relates to a method of vacuum-laminating a film-like adhesive on an inner-layer circuit pattern in a method of manufacturing a multilayered printed wiring board of a build-up system in which conductive circuit layers and insulating layers are alternately piled up.
2. Prior Art
In a known conventional method of manufacturing a multilayered printed wiring board, several prepreg sheets formed by impregnating glass cloth with epoxy resin in stage B are laminated/pressed as insulating adhesive layers on an inner-layer circuit board with a circuit formed thereon, and the layers are connected via through holes. In the method, however, since heating and pressure molding are performed during the laminating/pressing, a large scale equipment and a long time are required, which increases cost. Additionally, since the glass cloth having a relatively high permittivity is used in the prepreg sheet, reduction of interlayer thickness is limited. Another problem is that uncertainty of insulation is caused by migration among the through holes (CAF).
To solve the problem, recently technique for manufacturing a multilayered printed wiring board of a build-up system by alternately piling up organic insulating layers on conductive layers of an inner-layer circuit board has been noted. In Japanese Patent Application Laid-open No. 64960/1996, there is provided a method of applying an undercoat adhesive, tentatively drying, laminating a film-like additive adhesive, heating and hardening, roughing with alkaline oxidizing agent, and forming a conductive layer by plating to manufacture a multilayered printed wiring board. Moreover, in Japanese Patent Application Laid-open No. 202418/1995, there is disclosed a method of laminating, on an inner-layer circuit board, an adhesive copper foil obtained by forming an adhesive layer of polymeric epoxy resin and liquid epoxy resin on a copper foil to manufacture a multilayered printed wiring board. On the other hand, in Japanese Patent Application Laid-open No. 97927/1999, the present inventors have disclosed an interlayer adhesive film for a multilayered printed wiring board and a productive method of manufacturing the multilayered printed wiring board using the interlayer adhesive film, in which coating of an inner-layer circuit pattern and filling of surface via holes and/or through holes with resin can be performed simultaneously. When the adhesive films are vacuum-laminated under heating and pressurizing conditions, there is a problem that the adhesive bleeds from end portions of the adhesive films to soil press surfaces, because the adhesive is provided with thermal fluidity. To solve the problem, in Japanese Patent Application Laid-open No. 97927/1999, there is proposed a method of providing about 5 mm or more of a support base film portion with no resin on both ends or one end of the adhesive film to prevent the adhesive from bleeding. This method, however, has a disadvantage that the productivity in manufacturing the adhesive films is deteriorated.
An object of the present invention is to provide a method for easily reducing adhesive bleeding in a method of laminating, on a patterned circuit base, an adhesive film face of a laminate constituted of a support base film and an adhesive film, using a heatable and pressable vacuum laminating device.
As a result of various studies on a method of preventing the adhesive bleeding, it has been found that the adhesive bleeding can be prevented by providing a bleeding preventive sheet between at least one press plate of the vacuum laminating device and the support base film of the laminate in such a manner that the bleeding preventive sheet fails to spread out of any point of a surface periphery of the laminate and to stain with the bleeding to the surface of a laminating metal roll. The present invention has thus been completed.
Specifically, a first embodiment of the present invention provides a method of vacuum-laminating an adhesive film which comprises a supporting base film disposed on at least one surface of a pattern-processed circuit substrate and a resin composition having a thermal flowability and being in the solid state at normal temperature disposed on the surface of said supporting base film so that said resin composition is laminated under heating and pressing conditions,
said method comprising the steps of:
(1) sheeting said adhesive film having the same size as or a smaller size than that of said circuit substrate in a state wherein the surface of said resin composition in said adhesive film is allowed to provisionally partially adhere to one surface or both surfaces of said circuit substrate; and
(2) disposing a protecting film having an area larger than that of said adhesive film on said adhesive film provisionally adhering to said circuit substrate so that the center of said protecting film is disposed at substantially the same position as that of the center of said adhesive film, followed by vacuum laminating under heating and pressing conditions.
A second embodiment of the present invention provides an adhesive film vacuum laminating method, further comprising a post-treatment step in which said adhesive film is smoothed by heating and pressing using a pressing metal plate or a laminating metal roll which can be used even when a protecting film having an area larger than that of said adhesive film is disposed between said supporting base film and said pressing metal plate or laminating metal roll, wherein said adhesive film comprises said supporting base film and said resin composition having a thermal flowability and being in the solid state at normal temperature disposed on the surface of said supporting base film and is vacuum laminated in the order of supporting base film/resin composition/circuit substrate.